1. Field of the Invention
The invention is in the field of thermoelectric devices. The invention has special application to thermoelectric devices for heating and cooling air for human use which utilize thermoelectric modules associated with a heat exchanger.
2. State of the Art
Thermoelectric devices for heating and cooling based upon the peltier effect are well known in the prior art. Typically, a thermoelectric module is constructed of N-type and P-type semiconductor material, such as bismuth telluride. The N-type and P-type semiconductor material are electrically connected in series. When an electric current is passed through the circuit, heat is absorbed at the cold junction of the circuit and is transferred to the hot junction of the circuit. By associating the hot and cold junctions with a heat exchanger, heat can be transferred from one flow stream to another. Typically, the heat exchanger is filled with either gas or liquid media, thereby resulting in the heating of one media and the cooling of the other media.
Historically, practical applications of thermoelectric cooling and heating using thermoelectric modules have been primarily limited to small scale specialized uses because of high cost and energy inefficiencies. In the last 15 to 20 years, applications of thermoelectric modules have been developed to utilize them in large scale cooling of submarines and passenger trains. Utilization of thermoelectric modules in large scale applications has required development of various types of thermoelectric devices, which utilize thermoelectric modules associated with heat exchangers, which are designed for assembly with each other to provide the cooling and heating capacity required for large scale applications. One such prior art design for a thermoelectric device includes a parallel flow heat exchanger in association with thermoelectric modules. Another prior art design for a thermoelectric device is the "air to air cross-flow" design in which the conduits of the exchanger, which sandwich thermoelectric modules, are positioned relative to each other to allow for perpendicular flow of hot and cold air through the thermoelectric device. Typical of these thermoelectric devices are U.S. Pat. No. 3,626,704 issued to Coe on 9 Jan. 1970 and U.S. Pat. No. DE 1,801,768 issued to Newton in 1967.
The primary disadvantages of these prior art devices are lack of reliability and difficulty of service. In some prior art devices the electric current to the thermoelectric modules flows through the heat exchanger itself. To establish the electric circuit, the thermoelectric modules are electrically connected in series through the heat exchanger. In some prior art configurations, the electric connection is established by attaching a heat exchanger to the hot and cold junctions of the thermoelectric modules by soldering, thereby creating rigid physical connections between adjacent thermoelectric modules and between the heat exchanger. Since the heat exchanger conduit attached to the hot side of the thermoelectric modules and the heat exchanger conduit attached to the cold side of the thermoelectric modules are subject to different temperatures, they are expanding and contracting at different rates. This expansion and contraction differential creates a shear force across the thermoelectric modules, which may result in their breakage.
In an attempt to overcome these problems, a design, such as that typified by U.S. Pat. No. 3,726,100 issued to Widakowich on 10 Apr. 1973 was developed. In this design, the heat exchanger conduits are not soldered to the thermoelectric module, but the thermoelectric modules are sandwiched between the hot and cold heat exchanger conduits, with the hot and cold heat exchanger conduits compressed against adjacent thermoelectric modules by bolts such that the heat exchanger conduits are in electric and thermal contact with the thermoelectric modules to create an electric circuit through the heat exchanger conduits and semiconductor material such that they are connected in series. Since adjacent thermoelectric modules are still rigidly connected to each other, the shearing forces still exist to some extent.